A Look at the GM 6L80; Part 1 - ATRA

A Look at the GM 6L80; Part 1 

A Look at the 

GM 6L80; 

Part 1 

Introduction 

The first of ten 

new 6-speed automatics, 

the 6L80 was introduced 

for the 2006 model 

year (Figure 1). The 6L80 

(RPO MYC) is currently 

available in the Corvette; 

Cadillac XLR-V; Cadillac STS- 

V; Chevrolet, Cadillac and GMC C/K 

trucks; and the Hummer H2 platforms. 

Features 

• Input torque capacity: 430 lb-ft 

(583 Nm) 

• Output torque capacity: 664 lb-ft 

(900 Nm) 

• Ratios: 

1 st — 4.02:1 

2 nd — 2.36:1 

3 rd — 1.53:1 

4 th — 1.15:1 

5 th — 0.85:1 

6 th — 0.67:1 

Figure 1 

• M a x i m u m 

shift speed: 6500 RPM 

• Maximum GVW: 8600 lbs 

• Maximum GCVW: 14000 lbs 

• PRNDL positions: P, R, N, D, (S or 

M) 

• 2 shift solenoids (On/Off design): 

SS1, SS2 

• 6 PWM pressure control solenoids: 

PCS1, PCS2, PCS3, PCS4, PCS5, 

TCC 

Figure 2 Figure 3 

Cadillac STS-V 

Hydra-Matic 

2006 6L80 (MYC) 

Six Speed RWD 

Automatic Transmission 

by Steve Garrett 

• 32-bit TCM (TEHCM) mounted 

inside the transmission on the 

valve body (referred to as the control 

solenoid valve assembly). The 

TEHCM incorporates the TCM, 

solenoids, pressure switches and 

TFT, and is bolted to the valve 

body. 

• EC3 Converter 300mm (Corvette) 

258mm twin plate (XLR-V and 

STS-V) 

• Fluid required: Dexron VI 

• Clutch-to-clutch shifts; 5 clutches, 

1 sprag 

• Planetary assemblies: Input — 

Simpson; Output — Dual Pinion 

34 GEARS January/February 2008

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• Vane-style oil pump 

• Internally-mounted input and output shaft, and Hall 

Effect speed sensors 

• Internal Mode Switch (IMS) 

• Performance Algorithm Shifting (PAS) programming 

• Performance Algorithm Lift foot (PAL) programming 

• Sport mode and TAP shift 

• Adaptive strategies with fast learn capabilities 

• Up to 75 transmission-only DTCs 

Checking Fluid Level 

The 6L80 transmission requires an unusual process 

for checking its fluid level. Many 6L80 applications don’t 

have a dipstick; there’s a plug in the dipstick hole. The 

plug can be removed and the hole used as a fill point for 

transmission fluid (Figure 2). Here’s how to check the 

fluid level: 

Bring the transmission fluid temperature between 86º– 

122ºF (30º–50ºC). You can verify this using a scan tool, the 

driver information center, or the transmission gauge. 

If the transmission has a dipstick, use that to check the 

fluid level; on applications without a dipstick: 

• Park the vehicle on level ground. 

• Start the engine and let it idle. 

• Shift the transmission through each range, pausing in each 

range for about 3 seconds to give the clutches a chance to 

fill. 

• Place the transmission in park. 

• Remove the level control plug located in the transmission 

Figure 6 

Figure 4 

Figure 5 

oil pan. The fluid should drip out the level control 

hole. If so, the fluid level is okay. 

Ø If fluid doesn’t drip from the level control hole, 

add Dexron VI until fluid starts to drip from the 

hole. 

Ø If fluid runs from the hole, wait until the fluid 

stops running out to lower the fluid to the 

proper level. 

The level is correct when fluid drips from the hole. 

If a steady stream is present or no flow is present the 


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fluid level is incorrect. Readjust the 

fluid level, and reinstall the fill plug 

and the level control plug. 

You can add fluid through the dipstick 

hole or through the level control 

hole. 

What’s Inside? 

NSBU/PRNDL/IMS Switch 

(Figure 3)— The internal mode switch 

(IMS) is mounted to the valve body 

and is connected mechanically to the 

manual valve. Electrically the internal 

mode switch operates much like other 

GM applications: 

The TCM sends an 8.3–9.3 volt 

bias to the internal mode switch on 4 

circuits: A, B, C and P. Pin N, which 

is used for neutral starting operations, 

is fed system voltage from the ECM. 

As you move the range selector, the 

internal mode switch will ground or 

open the circuits or circuit required to 

indicate the specific manual valve position. 

The TCM identifies the range by 

the voltage sequence from the switch 

(Figure 4). 

Low = Grounded (0 Volts) 

High = Open (Source Voltage) 

Note: Not all applications will 

include all the ranges shown in the 

chart 

Input and Output Speed Sensors 

— The speed sensors are Hall Effect 

assemblies and are mounted to the 

control valve assembly (valve body). 

The TCM provides a signal voltage of 

8.3–9.3 volts for the sensor operation. 

As the clutch housings rotate, the sensors 

produce a square wave signal that 

varies frequency with the speed of the 

clutch housing (Figure 5). The TCM 

will monitor the frequency of the signal 

to determine the input or output speed 

(Figure 6 & 7). 

Control Solenoid Body and TCM 

Assembly (TEHCM) 

— The control solenoid 

valve assembly consists 

of these components: 

• 2 shift solenoids 

(On/Off design): 

SS1, SS2; 16-20 

ohms at 70ºF (21ºC) 

Figure 7 

• 6 controlled pressure control solenoids; 

PCS, PCS2, PCS3, PCS4, 

PCS5 and TCC; 3.0-5.5 ohms at 

70ºF (21ºC), 0.9-amp current limit, 

solenoid operational voltage from 

TCM 8.3–9.3 volts, cleaning pulse 

every 30 seconds during P/N. 

• 32-bit TCM (TEHCM); mounted 

inside the transmission on the 

valve body. Thermal protected 

290ºF (144ºC), default 3 rd or 5 th . 

• 4 pressure switches that monitor 

valve and clutch hydraulic operation 

and clutch volume index (CVI 

— adaptive learn) 

• A transmission fluid temperature 

sensor (TFT) NTC thermistor. 

• 2 TCM internal temperature sensors 

Figure 8 


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Pressure Switches — The pressure 

switches are housed as part of 

the control solenoid valve assembly. 4 

switches are used: 1, 3, 4 and 5. The 

switches provide an input to the TCM 

and have two basic functions: 

• To monitor clutch regulator valve 

and clutch hydraulic operation 

(Figure 8). 

• To monitor clutch volume index 

(CVI — adaptive learning). 

Solenoid Operation 

IMPORTANT: In systems using 

the Bosch solenoid system, ON/OFF 

refers to the solenoids’ hydraulic commanded 

position, not their electrical 

command as with other applications; 

more on this later. 

Shift solenoid and PCS operation 

is controlled by the TEHCM (TCM). 

The TCM regulates the feed voltage 

to the solenoids between 8.3–9.3 volts 

(Figure 9). The TCM then regulates 

the current flow through the solenoids. 

The shift solenoids are On/Off design 

with the TCM controlling the power 

and ground for the solenoids (Figure 

10). The pressure control solenoids are 

high-side, PWM controlled. The TCM 

is overcurrent and overtemperature protected 

(Figure 11, 12, &13). 

Bosch refers to the solenoids by 

their hydraulic operation: Normally 

High (NH) or Normally Low (NL). 

Normally High means the solenoid 

allows pressure to travel to the clutch 

when the solenoid is off. Normally 

Low means the solenoid prevents pressure 

from getting to a clutch when the 

solenoid is off. 

IMPORTANT: This concept of 

Normally High and Normally Low to 

describe solenoid operation is far more 

involved — and confusing — than it 

might initially appear. We’ll discuss 

the operation of the Bosch solenoids in 

detail in an upcoming issue of GEARS. 

The solenoids are protected by the 

filter plate. The filter plate is housed 

between the valve body and the control 

solenoid valve assembly (TEHCM) 

and must be replaced any time the 

valve body or control solenoid valve 

assembly (TEHCM) is replaced, or are 

unbolted from each other. 

Clutches 

The 6L80 transmission (Figure 14) 

uses three rotating clutches and two 

stationary clutches. 

1-2-3-4/Forward Clutch — This 

clutch is applied in 1 st through 4 th 

gears. The 1-2-3-4/forward clutch is 

located in the bottom of the reverse 

clutch housing. When applied, it locks 

the reverse drum to the 2-6 and 3-5reverse 

shell to drive the lower sun gear 

for the output carrier. 

2-6 Clutch — This is one of the 

stationary clutches. It’s located on top 

of the center support assembly. It prevents 

the 2-6 and 3-5-reverse shell from 

rotating. 

3-5-Reverse Clutch — This clutch 

is used in 3 rd , 5 th and reverse. It’s 

located in the reverse clutch housing. 

When applied, it connects the reverse 

drum to the 2-6 and 3-5-reverse shell. 

The clutch then drives the front output 

sun gear in the output carrier. 

4-5-6/Input Clutch — This clutch 

is located in the input housing. When 

applied, it locks the input housing to the 

4-5-6 drive hub, which drives the lower 

output carrier. 

Low/Reverse Clutch — This sta- 

Figure 9 

Figure 10 

Figure 11 

tionary clutch is located in the lower 

section of the center support. The Low/ 

Reverse clutch is used in reverse and 

manual low. 



Powerflow 

First Gear: 1-2-3-4/Forward 

clutch (rotating clutch) is applied. 

Engine torque is applied to the 

input shaft, which is the driving component 

for all ranges. When the input 

shaft rotates, it drives the input ring 

gear. The clutch drives the pinions of 

the input carrier, which is splined to the 

reverse drum. 

When the 1-2-3-4/Forward clutch 

applies, it transfers engine torque 

through the input shaft to the reverse 

drum. The torque then transfers to the 

1-2-3-4/input shell. The input shell is 

splined to the lower output sun gear. 

The sun gear drives the output carrier 

pinions, rotating the output ring gear at 

a 4.027:1 gear ratio. 

Second Gear: 1-2-3-4/Forward 

clutch (rotating clutch) and 2-6 (stationary) 

are applied. 

With the 2-6 clutch applied, the 

2-6 and 3-5-reverse shell can’t rotate. 

With the shell locked to the case, the 

upper output sun gear is held. Engine 

torque is still being applied through the 

1-2-3-4/Forward clutch, which drives 

the lower sun gear. The combination 

of the two gearsets provides a 2.364:1 

gear ratio. 

Third Gear: 1-2-3-4/Forward 

clutch (rotating clutch) and 3-5-Reverse 

clutches (rotating clutch) are applied. 

With the 3-5-Reverse clutch applied, 

the reverse drum is locked to the 2-6 

and 3-5-Reverse shell. Engine torque is 

now transferred through both sun shells, 

driving the output sun gears and output 

carrier. The pinions rotate, turning the 

output ring gear at a 1.532:1 ratio. 

4 th Gear: 1-2-3-4/Forward clutch 

(rotating clutch) and 4-5-6/Input clutches 

(rotating clutch) are applied. 

With the 4-5-6/Input clutch applied, 

the hub is driven at engine speed. The 

1-2-3-4/Forward clutch is still applied, 

rotating the lower output sun gear, 

which rotates the ring gear at a 1.152:1 

ratio. 

5 th Gear: 4-5-6/Input (rotating 

clutch) and 3-5-Reverse clutches (rotating 

clutch) are applied. 

The 1-2-3-4/Forward clutch releases. 

The 3-5-Reverse clutch is now 

applied, driving the upper sun gear in 

the output gearset. At the same time, 

engine torque travels through the 4-5- 

6/Input hub, driving the carrier, which 

creates an overdrive ratio of 0.852:1. 

6 th Gear: 4-5-6/Input (rotating 

clutch) and 2-6 clutches (stationary) 

are applied. 

With only the 4-5-6/input clutch 

applied, all of the engine torque travels 

through the output carrier with an overdrive 

ratio of 0.667:1. 

Reverse: 3-5-Reverse (rotating 

clutch) and Low/Reverse clutches (stationary) 

are applied. 

With the 3-5-Reverse clutch 

applied, engine torque from the input 

shaft is sent through the input gear 

set, through the reverse drum, to the 

2-6 and 3-5-Reverse sun shell. The 

upper sun gear rotates the pinions. 

The carrier attempts to rotate, but the 

Low/Reverse clutch is also applied, 

holding the carrier stationary. This 

causes the ring gear to rotate backward 

at a 3.064:1 ratio. 

Figure 13 

Figure 14 

That’s enough for this issue; in 

the next issue of GEARS, we’ll look at 

some of the diagnostic processes for 

these units. 

Figure 12 


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A Look at the GM 6L80; Part 1 - ATRA

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